Recent studies demonstrate widespread pesticide exposures to pregnant women, fetuses, and young children. We have documented pesticide exposures to primarily low-income Latina pregnant women and their children. Pregnant women in our population had higher urinary metabolite levels compared to national eference data; metabolite levels were also higher immediately after birth, suggesting that physiological changes at parturition could increase neonatal exposures. We have also found that nearby pesticide use, the presence of farmworker household members, and the consumption of fruits and vegetable was associated with higher metabolite levels in infants. Our Specific Aims for the next five years are: (1) to evaluate changes in pre- and postpartum maternal pesticide excretion and to develop PBPK models describing the peripartum period; (2) to identify the best and most convenient biological media for assessing exposure to OP pesticides in children; (3) to quantify the relative contribution of diet to children's OP pesticide exposures in agricultural and urban communities; and (4) to characterize urinary OP metabolite levels in preschool and school-aged children and identify correlates of exposure. To meet Aim 1, we will enroll 30 women planning delivery by Cesarean section and analyze OP pesticides or metabolites in urine, blood, and breastmilk collected in the peripartum period. We will develop pregnancy-parturition-neonate PBPK models. To meet Aim 2, we will measure pesticides metabolites in 24-hour, first morning void, and random spot urine and saliva samples from 25 children and determine how well OP metabolite levels in the 24-hour "gold standard" measure are represented by alternative matrices. To meet Aim 3, we will conduct a two-phase cross-over trial, randomly assigning 20 children in an urban community and 20 children in an agricultural community to an organic or conventional diet for one week each. To meet Aim 4, we will measure OP pesticide exposure to children at ages 42 and 60 months and determine which factors, such as child age, home or agricultural pesticide use, season, or occupation of household members best predict these exposures. This continuation provides a unique opportunity to prospectively examine OP pesticide exposures to primarily Latino farmworker children living in an agricultural community. The overall goal of the Exposure Project is to identify the most important pesticide exposure pathways to young children so that effective and age-appropriate interventions and policies can be designed and implemented.